1. Field of the Invention
The present invention relates to a thin film magnetic recording head with an inset insulation layer that defines zero throat level with a substantially perpendicular apex angle and more particularly to such a recording head with a first insulation layer in a notch milled in a first pole piece layer of the head to define the zero throat height of the head with substantially flat topography at the front of the head.
2. Description of the Related Art
A thin film inductive write head includes one or more coil layers embedded in an insulation stack, the insulation stack being sandwiched between first and second pole piece layers. A write gap is formed in a pole tip region by provision of a gap layer between the pole pieces. The pole pieces are magnetically coupled in a back gap region. Between the pole tip region and the back gap region is a yoke region where the pole piece layers separate from one another to accommodate the insulation stack. The insulation stack typically includes a first insulation layer (I1) on the first pole piece layer one or more coil layers on the first insulation layer, a second insulation layer (I2) over the coil layer and a third insulation layer (I3) over the second insulation layer.
A combined head, such as a merged magnetoresistive (MR) head, includes the aforementioned write head as a write head portion combined with an MR read head portion. The MR read head portion includes an MR sensor which is sandwiched between first and second gap layers which are, in turn, sandwiched between first and second shield layers. In a merged MR head a single layer serves a double function as a second shield layer for the read head and as a first pole piece for the write head. The combined head is carried on a slider which, in turn, is mounted on a suspension in a magnetic disk drive. The suspension is mounted to an actuator which moves the combined head over selected tracks on a rotating disk for reading and writing signals thereon. As the disk rotates a cushion of air is developed to provide an air bearing between the disk and the slider which counterbalances a loading force exerted by the suspension. A surface of the slider facing the disk is called an air bearing surface (ABS) and is typically spaced from the disk in the order of 0.050 .mu.m when the disk is rotating.
In the fabrication of a thin film magnetic write head it is important that zero throat height (ZTH) be accurately located. The zero throat height is the distance along a normal to the ABS between the ABS and a first location where the first and second pole piece layers separate due to topography of one of the insulation layers in the aforementioned insulation stack. Typically, an apex of the first insulation layer defines the ZTH. The apex is the foremost end of the first insulation layer closest to the ABS. The first insulation layer is hard baked resist which imposes on the layer an upwardly sloping surface which commences at the apex forming an apex angle with the plane of the write gap layer. Accordingly, the sloping surface of the first insulation layer angles toward the second pole piece, causing an angled separation of the first and second pole piece layers which commences at the apex. The apex angles of the first, second and third insulation layers cause pronounced slopes which rise from the ZTH and face the pole tip region. After hard baking these layers high optical reflectivity presents a problem in the fabrication of the second pole tip.
For good magnetic operation, it is important that the sidewalls of the second pole tip be planar and perpendicular to the ABS. When these sidewalls are irregular a portion of the write signal is induced into adjacent disk tracks, causing overwriting. One remedy is to make the tracks wider; however, this reduces the storage density of the disk. Therefore, in order to maintain high storage density, the art has endeavored to make the sidewalls of the pole tip regular. Two design considerations make this endeavor difficult. First, the first and second pole piece layers must separate as near as possible to the ABS in order to minimize flux transfer between the pole tips behind the ABS. This requires that the distance between the ABS and the zero throat height (ZTH) be minimized. Second, the second pole piece should widen as near as possible to the ABS to minimize saturation of the second pole tip. This widening commences at the "flare point". The ZTH is typically located between the ABS and the flare point. When both the ZTH and the flare point are close to the ABS, the optical reflectivity of the front slope of the insulation stack presents a problem in the fabrication of the second pole tip.
The second pole tip is constructed by spinning a thick photoresist layer on top of the insulation stack, over the site for the second pole tip. Ultraviolet light is then directed onto the photoresist through a mask which outlines the shape of the second pole tip. In the prior art, the flare point is behind the ZTH, over the front sloping reflective surface of the insulation stack. That portion of the ultraviolet light which is directed behind the flare point is reflected from the front slope of the insulation stack, enlarging the exposure of the photoresist on each side of the intended sidewalls of the second pole tip. When the photoresist is developed, the photoresist mask at the second pole tip region may be undesirably wide. This undesirably widens the second pole tip which leads to its irregularity.
Another problem in the fabrication of thin film magnetic recording heads is the inaccurate placement of ZTH as mentioned hereinabove. Relatedly, combined heads are typically fabricated in batches on wafers using thin film techniques. At a known stage (the "row level"), a wafer is sliced into rows, with each row comprising a 1.times.N array of combined heads. Each row is lapped to form an ABS for each head in the row. In each head the MR stripe of the read element and the read gap of the write element intersect the ABS. Lapping continues until the ABS is as close as possible to establish the final electrical resistance of the MR stripe. Ideally, the ZTH and the end of the MR stripe in the read element should be finalized at selected locations. Unfortunately, the initial location of the ZTH at the apex of the first insulation layer is typically altered by post processing of a head. After fabrication, the first insulation layer is sputter cleaned in preparation for a seedlayer which is employed to fabricate the coil layer. This first sputtering step removes some of the first insulation layer and alters the location of its apex. After cleaning, the seedlayer is deposited and masked for the coil layer. Unwanted seedlayer portions are removed by a second sputter step. The second sputter step again removes a portion of the first insulation layer, altering the location of its apex. After formation of the final insulation layer, the insulation stack is sputter cleaned in preparation for a seedlayer employed for fabricating the second pole piece. This third sputter step again removes a portion of the first insulation layer and alters the location of its apex. After these sputter steps the apex of the first insulation layer, and thus ZTH of the head, can be recessed as much as 0.25 .mu.m into the head away from its intended location in an uncontrollable way.
A further problem with the insulation stack is its proximity to the ABS. Unfortunately, the coefficients of expansion of the materials of the insulation stack and the pole piece layers are markedly different. When the write head is operated the coil layers generate heat, which causes expansion of the insulation stack and pole pieces. The material of the insulation stack expands more than the pole piece material, causing the pole tips to protrude beyond the ABS of the slider. This same expansion of the insulation stack can cause an overcoat layer of the head to crack.
Accordingly, there is a strong felt need to overcome or minimize the aforementioned problems associated with prior art inductive write heads.